Method and system for sending acknowledgement character message in time division duplex system

The invention provides a method and system for sending an acknowledgement character message in a time division duplex system, which are suitable for being configured in a terminal for feeding back a hybrid automatic retransmission request acknowledgement character message (HARQ-ACK) by adopting a physical uplink control channel (PUCCH). The method comprises the steps of: receiving a physical downlink sharing channel (PDSCH) from a service cell in a binding window; when one PDSCH without the PDCCH and one PDSCH corresponding to the PDCCH with a downlink allocation index value equal to 1 of a main service cell are received in the binding window, feeding back a corresponding HARQ-ACK according to one of the following modes: feeding back a corresponding HARQ-ACK by adopting a PUCCH format 3, feeding back a corresponding HARQ-ACK by adopting a PUCCH format 1b, and feeding back a corresponding HARQ-ACK by combining a PUCCH format 1b with a channel selection mode. The invention does not influence the traditional protocol.